In press filter devices and the like, a filter chamber is formed between two adjacent recess plates by the recess of at least one of the recess plates. Filtrate is discharged from the filter chamber through outlets into two separate filtrate collecting ducts, leading back to a head piece of the filter device. A Drying gas is piped from the head piece through one of these filtrate collecting ducts and outlets into the filter chamber and discharged through the other duct and filtrate collecting duct back to the head piece.
The drying gas is under pressure when piped into the filter chamber, and pushes the remaining liquid through a filter cake formed on a filter media in the filter chamber. After permeating the cake, the drying gas pressure falls down to ambient pressure and the drying gas expands, accordingly. For piping the expanded drying gas from the filter chamber back to the head piece, the related filtrate collecting duct either requires significantly larger pipes than the duct that pipes the pressurized drying gas from the head piece to the filter chambers, or the expanded drying gas flows at a significantly higher speed. In the former case, the related pipe cross section is unavailable for the filter chamber and thus decreases filtration capacity of the filter device. In the latter case, the increased speed of gas flow causes erosion and wearing of the recess plate.
Recess plates according to prior art have filtrate taps for manually opening the filtrate ducts to the ambience, for testing purposes, during a filtration cycle. Comparing opacity of the filtrate protruding from the taps provides for a simple but however qualitatively sensitive visual performance check of the related filter cloths. Moreover, in some filter devices according to prior art filtrate is always disposed straight from the filter chambers through the base body of the respective recess plates, to the ambience. However, such filter devices do not provide for drying the filter cake.